On the Manoeuvrability of Ships while Stopping by Adverse Rotation of Propeller : 1st Report

Abstract

It is well known that the ship is forced to deviate from her course when it is decelerated by rotating her propeller in the adverse direction. This paper clarifies the characteristics of unbalaced hydrodynamic forces caused by the propeller running astern when the ship has forward speed. First, the influences of ship speed and number of revolution on the quantitative and qualitative characteristics of unbalanced hydrodynamic forces are examined by model tests, when the ship travels in a straight course without sway and yaw motions. Secondly, the effects of sway and yaw motions are discussed according to the experimental results by the circular motion tests. As a result, it is concluded that when the ship has no transverse motion, unbalanced hydrodynamic forces can be regarded as a function of J_P(=U/nP) and the effects of transverse motions can be expressed well by an equivalent sideslip velocity v'_s at the stern defined by v'-r'/2. Lastly, the course stability of ships while stopping by adverse rotation of propeller is discussed. Our conclusion that the strong race of propeller with adverse rotation makes the ship more unstable coincides with the experimental results obtained by Wagner Smitt and Chislett in 1972.